<template>
  <div class="grid-view" ref="gridView">
    <slot></slot>
  </div>
</template>

<script>
  export default {
    name: "GridView",
    props: {
      cols: {
        type: Number,
        default: 2
      },
      hMargin: {
        type: Number,
        default: 8
      },
      vMargin: {
        type: Number,
        default: 8
      },
      itemSpace: {
        type: Number,
        default: 8
      },
      lineSpace: {
        type: Number,
        default: 8
      }
    },
    mounted() {
      setTimeout(this._autoLayout, 20)
    },
    updated() {
      this._autoLayout()
    },
    methods: {
      _autoLayout() {
        // 1.获取gridEl和children
        // 注: 这里为什么不用document.querySelector呢?
        // 答: 因为如果在项目中, 多处都用到了grid-view, 那么这里就不确定获取的是哪一个了.
        let gridEl = this.$refs.gridView;
        let children = gridEl.children;

        // 2.设置gridEl的内边距
        gridEl.style.padding = `${this.vMargin}px ${this.hMargin}px`

        // 3.计算item的宽度
        let itemWidth = (gridEl.clientWidth - 2 * this.hMargin - (this.cols - 1) * this.itemSpace) / this.cols;
        for(let i = 0; i < children.length; i++) {
          let item = children[i];
          item.style.width = itemWidth + 'px';
          if((i + 1) % this.cols !== 0) {
            item.style.marginRight = this.itemSpace + 'px'
          }
          if(i >= this.cols) {
            item.style.marginTop = this.lineSpace + 'px'
          }
        }
      }
    }
  }
</script>

<style scoped>
  .grid-view {
    display: flex;
    /*根据宽度决定一行中显示多少个*/
    flex-wrap: wrap;
    /*均等分*/
    justify-content: space-around;
  }
</style>
